Sen—Two astronauts completed a marathon six hour 41 minute spacewalk outside the International Space Station (ISS) today to prepare the orbiting outpost for the arrival of future commercial crewed spacecraft.

NASA’s Barry “Butch” Wilmore and Terry Virts completed all the tasks required for the first of three EVAs and managed to get started on the list of to-do’s for the next which is due on Wednesday.

They were working to lay cables along the front of the US segment that will provide power and communication to two International Docking Adaptors to be sent to the ISS in June. Those will allow crew-carrying commercial spacecraft flown by SpaceX and Boeing to dock with the ISS when they launch from Florida from 2017 onwards.

Expedition 42 Commander Wilmore and Virts managed to complete eight out of ten cables, deploying 340ft of 360ft of cable that has to be laid to reconfigure the ISS for the new arrivals. Virts was making his first spacewalk and Wilmore his second.

After just two and a half hours, they had already finished attaching several cables to the port side of the Pressurized Mating Adapter-2 beneath two debris shields, before moving to attach another to the starboard side.

Engineers at mission control were delighted with the progress made by the astronauts. The only concern came when levels of carbon dioxide were seen to rise in Wilmore’s suit towards the end of the EVA. NASA agreed with him that this was due to his over-exertion in trying to undo a stubborn connector.

It happened towards the end of the spacewalk—the 185th carried out at the ISS—when Wilmore was releasing four connectors that were used to connect the Space Shuttle with the Harmony module before that spacecraft was retired from service. The fourth proved troublesome but eventually came free.

The new configuration of the ISS will allow the arrival of flights that will boost the size of the station’s standard crew from six to seven and double the amount of time that they can devote to research.

The spacewalk officially began at 1245 UTC (7:45 am EST) and ended at 1926 UTC (12:45 pm EST). Once they were safely back in the airlock, ESA astronaut Samantha took charge from within the ISS, welcoming her crewmates back.